Quadrature amplitude modulation (QAM) has found extensive applications in wired and wireless digital communications systems. In a digital QAM scheme, the QAM constellations are specified by both their amplitude and phase in a quadrature coordination. Phase-shift keying (PSK) modulation can be considered as a special case of QAM where the amplitude of a PSK modulation scheme is constant and the PSK constellations are equally spaced on a circle.
The aim of digital QAM is to communicate a message from a transmitter to a receiver. However, such communication must contend with the presence of noise, such as thermal noise and phase noise, as well as other limitations such as transmitter power limitations. Phase noise (frequency offset) is particularly problematic at higher frequencies, such as 60 GHz and above, and can be generated due to imperfect oscillators in both transmitter and receiver. Use of higher-order QAM in the presence of thermal noise, phase noise, and other limitations, can result in unacceptably high error rates, particularly for higher-frequency communication systems.
Therefore, there is a need for a method and apparatus for quadrature amplitude modulation that obviates or mitigates one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.